Chimney Top Calculators

Na-22 dose rate & shielding calculator

Dose rate from a Sodium-22 point source at any distance, with shielding — or solve for activity, distance or shield thickness. Γ = 1.2 R·m²/(Ci·h), half-life 2.602 years.

Calculator

Calculated — choose the unit for the result.

Calculated — choose the unit for the result.

When solving for shield thickness this is the target dose rate behind the shield.

Calculated — choose the unit for the result.

Results

Dose rate
1,200 mR/h
Exposure rate
1.2 R/h
Air-kerma rate
10.52 mGy/h
Dose-equivalent rate (≈, 1 R ≈ 1 rem)
12 mSv/h · 1.2 rem/h
Activity
1 Ci · 37 GBq
Distance
1 m · 3.281 ft
Γ used
1.2 R·m²/(Ci·h)

About Sodium-22

PET scanner calibration and instrument check sources.

Principal photons: 1274.5 keV (99.94 %), 511 keV annihilation (180 %). Specific gamma-ray constant used here: 1.2 R·m²/(Ci·h) (12 R·cm²/(mCi·h)).

Unshielded exposure rate by distance

Activity0.3 m1 m2 m5 m10 m
1 mCi (37 MBq)13.3 mR/h1.2 mR/h0.3 mR/h0.048 mR/h0.012 mR/h
1 GBq (27 mCi)360 mR/h32.4 mR/h8.11 mR/h1.3 mR/h0.324 mR/h
1 Ci (37 GBq)13,300 mR/h1,200 mR/h300 mR/h48 mR/h12 mR/h

Multiply mR/h by 10 for an approximate µSv/h figure (1 R ≈ 10 mSv for photons).

The formula

Ẋ [R/h] = 1.2 × A [Ci] × T / d² [m²]

T is the shield transmission (1 with no shield). See the main calculator page for the full derivation and assumptions.

Worked example

A 10 mCi Na-22 source at 2 m: Ẋ = 1.2 × 0.010 / 2² = 3 mR/h. Halving the distance to 1 m quadruples it to 12 mR/h.

Frequently asked questions

What is the dose rate at 1 meter from 1 Ci of Na-22?
About 1,200 mR/h (1.2 R/h) for an unshielded point source, using Γ = 1.2 R·m²/(Ci·h). That is roughly 12 mSv/h with the 1 R ≈ 10 mSv photon convention.
What is the gamma constant of Na-22 in SI units?
About 0.324 µSv/h at 1 m per MBq (approximate dose-equivalent rate), or 12 R·cm²/(mCi·h).
What is the half-life of Na-22?
2.602 years (ENSDF evaluated value via NuDat 3). Use the decay calculator to correct a source's activity to today's date before computing a dose rate.
Is there shielding data for Na-22?
The broad-beam table used by this site (NCRP Report 49) does not list Na-22. Choose "Custom HVL" in the calculator and enter a half-value layer from a reference appropriate to its photon energies.

Sources

  1. Unger, L. M. & Trubey, D. K. (1982). Specific Gamma-Ray Dose Constants for Nuclides Important to Dosimetry and Radiological Assessment. ORNL/RSIC-45/R1, Oak Ridge National Laboratory. www.osti.gov
  2. U.S. Department of Health, Education, and Welfare (1970). Radiological Health Handbook, revised edition. Public Health Service, Bureau of Radiological Health.
  3. National Nuclear Data Center, Brookhaven National Laboratory. NuDat 3 (ENSDF evaluated half-lives and photon emission data). www.nndc.bnl.gov
  4. ICRU Report 85 (2011). Fundamental Quantities and Units for Ionizing Radiation. (Mean energy per ion pair in dry air, W/e = 33.97 J/C.)